Compounds having strong light absorption at specific wavelengths are used as optical elements in optical filters for image display devices such as liquid crystal displays (LCDs), plasma display panels (PDPs), electroluminescence displays (ELDs), cathode-ray tube displays (CRTs), fluorescent display tubes, and field emission displays, and in optical recording layers of optical recording media such as DVD±Rs.
Such compounds are used e.g. as light absorbers when employed as optical elements in optical filters for image display devices. Image display devices create color images by combining light in the three primary colors, red, blue, and green, but the beams used for creating the color images include light that impairs display quality, such as 550- to 620-nm light between green and red, and also include 750- to 1100-nm light that possibly causes malfunction of infrared remote controllers. Thus, optical filters are required to have a function of selectively absorbing light in such unwanted wavelengths, and also a function of absorbing light ranging from 480 to 500 nm and from 540 to 560 nm in order to prevent reflection and glare of external light from fluorescent lamps etc. In image display devices and the like, therefore, optical filters containing light-absorbing compounds (light absorbers) that selectively absorb light at such wavelengths are used.
In recent years, there has also been a demand for light absorbers that can selectively absorb near-infrared rays particularly ranging from 800 to 1000 nm in order to provide display elements with sufficient color purity and color separation and thus achieve high image quality. Near-infrared-ray absorbing materials containing such light absorbers are widely used for optical filters as well as for other materials, such as photosensitive materials for laser welding, laser blocking materials, and heat-ray blocking materials. These near-infrared-ray absorbing materials used in such applications are expected to absorb light only within the targeted range—i.e., have a narrow half-width at λmax and an extremely sharp light absorption—and also have the ability to maintain their functionalities even when subjected to light and/or heat, for example.
Various optical filters containing light absorbers are known. For example, Patent Document 1 discloses a near-infrared-ray absorbing film having a near-infrared-ray absorbing layer containing, as essential components, a cyanine compound and a diimmonium compound having specific structures. Patent Document 2 discloses a near-infrared-ray absorbing optical filter containing a metal complex having a specific structure. Patent Document 3 discloses a near-infrared-ray blocking filter containing a diimmonium salt. Patent Documents 4 and 5 disclose cyanine compounds having an absorption maximum near 900 nm. The compounds used for these near-infrared-ray absorbing films and filters, however, have insufficient performance: for example, the absorptivity exhibits poor light resistance in the range between 800 and 1000 nm, and the absorption is large in the visible region.
Patent Document 6 discloses an optical recording material containing a cyanine compound having a specific group. The document, however, contains no concrete disclosure on compounds having an absorption maximum in the range between 800 and 1000 nm, nor does it teach anything about using the disclosed compound as a near-infrared-ray absorbing material.
Further, Patent Document 7 discloses the use of a phthalocyanine compound as a near-infrared-ray absorbing material for laser welding of plastics. To absorb laser beams with higher efficiency, however, colorant compounds with a higher ε are desirable.